The instant invention relates to the field of sewing machines, and particularly to industrial sewing machines for use in specialized operations.
Both special purpose and general purpose sewing machines are well known in the prior art. General purpose sewing machines are machines characterized as being capable of basically straight stitching, with patterns and the like being created through the use of such machines by manually manipulating the material as desired to result in the desired stitching. Such machines may include adjustments for determining the length and other characteristics of the stitch, though all such machines are intended for manual guidance and manipulation of the material as well as manual control of the machine operation to achieve the desired end result.
The special purpose machines are generally machines for semi-automatically achieving the desired stitch without the attendant manual manipulation of the material. Certain machines of this type are referred to as tackers, which may be used to sew pockets, buttonholes and the like, merely by placing the material at a predetermined starting position with respect to the needle and activating the sewing machine, whereby the machine will cause the material to generally advance through a predetermined path to create the stitch desired.
Prior art special purpose machine as are commonly in use have certain undesirable characteristics. Since they must not only sew but trace out variable patterns depending upon some variable pattern determining means, such machines are generally more expensive than ordinary sewing machines and are limited to certain predetermined operations. They cannot be used for general sewing purposes. Consequently, such machines represent a substantial investment in equipment which is not available for general use and can only be justified in those instances where a sufficient use of such machines can be made. Also, in the prior art special purpose machines, the means for determining the pattern to be sewn is comprised of a changeable cam system, generally located under the machine. Accordingly, a special cam, itself being relatively expensive, must be made for each different pattern to be sewn by the machine. Furthermore, the cam system is generally buried within the mechanical assemblage of the machine so that the changing of cams requires a substantial amount of time of a skilled mechanic, representing a substantial cost in the cam mechanic's time and the loss of use of the machine while a change is being effected.
There is thus a need for a system whereby the function of a special purpose machine may be achieved, preferably by an attachment to a conventional machine, whereby variations in the pattern sewn may readily be achieved by the operator as desired, where the fabric is firmly grasped so as to be caused to accurately move to traverse the predetermined pattern, and whereby the machine may be used for general sewing requirements when not in use for special purposes.
It is known to convert conventional sewing machines to perform specialized operations heretofore only achievable on special machines. A clamp system clamps the fabric in functional disposition with respect to the needle of the sewing machine, with a two dimensional drive system having orthogonal tables advancing the fabric clamp and thereby the fabric through a predetermined pattern so as to automatically sew buttonholes, pockets and the like. The two dimensional drive system is actuated by means of a stepper motor operative when the needle is withdrawn from the material so as to incrementally step the fabric between stitching cycles, thereby allowing the fabric to remain stationary while each stitch is being made. For this purpose, a sensor is provided on the sewing machine to synchronize the fabric advance system with the sewing machine operation. The sensor provides a signal to a conventional logic and servo system.
Special purpose industrial sewing machines operating at high speeds, such as 3000 or more stitches per minute, impose severe system requirements for quality sewing. Experience has shown that none of the prior art clamping and two dimensional driving systems are capable of meeting the severe system requirements for quality sewing, primarily for lack of structural rigidity and excessive inertia forces present in the system. The excessive inertia forces come about basically due to the fact that at least one of the drive motors is mounted on one of the orthogonal tables, and that the motor required to drive such a table is large, generally weighing in excess of ten pounds. The instant invention overcomes the problems of the prior art clamping and two dimensional driving systems by providing a novel clamp and a low inertia, two dimensional driving system which eliminates the need for one of the drive motors to be mounted on one of the orthogonal tables.